Herbicidal method using 2-chloro-3-mercaptopropyl n, n-substituted thiolcarbamates

ABSTRACT

BY A METHOD OF SYNTHESIS BASED ON A SECONDARY AMINE, CARBON DISULFIDE AND EPICHLOROHYDRIN THERE ARE PRODUCED 2,3-EPITHIOPROPYL N,N-DIALKYLTHIOLCARBAMATES WHICH ARE USED AS SELECTIVE HERBICIDES, PARTICULARLY IN PRE-EMERGENT CONTROL OF GRASSES SUCH AS BROME AND VOLUTEER OATS.

United States Patent US. Cl. 71-100 3 Claims ABSTRACT OF THE DISCLQSURE By a method of synthesis based on a secondary amine, carbon disulfide and epichlorohydrin there are produced 2,3-epithiopropyl N,N-dialkylthiolcarbamates which are used as selective herbicides, particularly in pre-emergent control of grasses such as brome and volunteer oats.

This application is a division of application Ser. No. 625,603, filed Mar. 24, 1967, now U.S. Pat. NO. 3,510,290.

SUMMARY OF INVENTION It is known that reaction of carbon disulfide with a secondary amine readily produces the amine salt of a corresponding dithiocarbamate, as illustrated below:

The product obtained by this reaction is often employed in manufacturing dithiocarbamate salts and esters.

It has now been discovered, however, that by reaction of an N,N-disubstituted dithiocarbamic acid or its salts with epichlorohydrin, valuable herbicidal products are produced which are not dithiocarbamates but which apparently result from a combined esterification and intramolecular rearrangement. The course of the reaction is illustrated as follows:

R (unstable) R fl) C1 The product possesses very selective herbicidal activity against a few grasses, particularly brome and oats, and is readily converted to the corresponding epithio ester which possesses similar herbicidal activity and greater chemical stability:

Patented Feb. 9, 1971 'ice The highly selective pro-emergent phytotoxicity of the novel compositions is particularly useful for application at the time of planting such crops as alfalfa and corn. Certain specific compounds of the group may also be applied at the time of planting soybeans and cotton. The preferred selective pre-emergent herbicides are 2,3-epithiopropyl N,N-dihydrocanbon substituted thiolcarbamates in which the two hydrocarbon substituents contain a total of less than ten carbon atoms. The hydrocarbon substituents may include alkyl, cycloalkyl from cyclopropyl to cyclohexyl and lower alkenyl groups.

DETAILED DESCRIPTION (I) Synthesis methods The compounds of the series, 2,3-epithiopropl N,N dialkylthiolcarbamates, are prepared by two general methods, one a three-step process, with isolation of intermediates and the other essentially a single-step process.

Method A 00 NH cs2 ClCH2CH----CH2 III II The initial low temperature reaction is believed to include reaction of epichlorohydrin with N,N-dialkyldithiocarbamic acid.

also be a metal salt, as well as an amine salt) appears to require a higher temperature than reaction with the acid.

In an experiment in which both routes were used to prepare the same N,N-diethyl thiolcarbamate compound, the yields were roughly equivalent. In syntheses based on morpholine, dicyclohexylamine or isopropyl cyclohexylamine as starting materials, Method B has been found to be the only successful route, with the dithiocarbamate salt being the sole product obtained in the first step of Method A, rather than the more reactive free acid.

Intermediates I and II are isolable, though not easily purified. I is thermally unstable, rearranging to II in a matter of several hours to several days, depending on the nature of the N substituents. The structure of I is thought to be as shown, based on its infrared spectrum and the NMR spectrum of its phenylurethane derivative. Intermediate II is relatively stable and suitable for herbicidal use, various type II compounds showing qualitatively the same activity as the corresponding type III compounds. The structure of II is not firmly established but present evidence favors the structure shown in the reaction diagram below.

essentially 3'chloro-2-hydroxypropy1 N,-N-diethyldithiocarbamate, (I; 'R,'R"=Et), a viscous yellow oil with no 01 R O detectable unreacted starting materials present. I1 I aN H Heating of the reaction mixture for 2 hours at 80-90 SOHZOHCHZSH NOSOH HZ 5 under vacuum gives 110 g. of crude rearrangement prod- R' II R III uct II (R,'R'=Et). The course of the rearrangement may be easily followed by the disappearance of infrared ab- QHWOOI sorption bands at 2.95,. (OH) and -10.1s,.-(c=s with R O the appearance of bands at 3.92 11. (SH) and 6.0 .1. ((1:0). The rearrangement is also accompanied by a marked de- /NCSCH2CHCH2SCCH3 crea e in viscosity R IV To 29 g. (0.12 mol of the crude rearranged product in On treatment with acetyl chloride both II and III give 100 ether q slowly 12 mol) of mcompounds (IV) having the same NMR spectrum and ethylamme. Reactlonus immediate, causing the ether to while this spectrum is not readily interpreted, and a mix- 15 reflux gepfly and pyeclpltalmg of methylamme hyture of position isomers cannot be excluded, comparison i solutlon 1S filtered eYaporamd and with model compounds suggests this structure shown. I dlstlued glvmg 6.614% yleld Overall) of 2 The success of this sequence of reactions leading'to a eplthlopropyl NgN'dwthylthlolcarbamate (HI); Rik: thiolcarbamate apparently requires a secondary amine as I702 119*20 h d B starting material. In three instances in which a primary Met 0 amine was used the crude products decomposed extensive- A l ti n f 36 (0,173 ol) of diethylammoninm ly and no epithiopropyl thiolcarbamate was P diethyldithiocarbamate and 15.0 g. (0.162 mol) .of epitained- In one experiment, starting with tert-butyl amlne. chlorohydrin in 100 m1. of dioxane is heated to reflux. y isothiocyanate Was found among the Products Shortly after heating is be un, a crystalline preci itate apg p of decomposition. pears. After two hours, the solution 1s cooled and filtered The final Products of the Sequence aIe dlstlllif-ble to recover 15.4 g. of diethylamine hydrochloride. The liquids or crystalline solids. Some care must be exercised filtrate i vacuum di ill d to remove the l f h 1- to prevent excessive heating during distillation. Otherwise vent, leaving 33.2 g. of a viscous brown Oil- Extra tion the following decompo ition readi y O urs: of this oil with ether, decantation and evaporation of the R O s O ether gives 25.7 g. of residue, distillation of which gives l Heat l 17.7 g. of III, R,R-=Et. NTJJSCHQCHJJE S In Table I are listed the compounds of type III pre- 1 pared by the above procedures.

TABLE I l N- S CH G-CH2 RI Percent R R Method yield 3.1. or M.P.

61.4 119-20/0.2 mm. a 11020/1.2 mm

133-4/1.2 mm. 117-1s/0.4 mm. Hexyl exyl A 128-60/0.8 mm.

-CH;CHgOCH2CH2 B B 74-5 h Meth e5-107/0.3 mm.

12s-33/0.1 mm

Crude material, not distillable up 1.5974. Crude material, not distillable nn 1.5773. 157-66/0.10.9 mm.

Crude mateiral, not distillable no 1.6142. Crude material, not distillable on 1.5763. Crude material, not distillable no 1.5581. Crude material, not distillable 111) 1.5156. M.P. 55.558 b Crude material, not distillable nn 1.5500. M.P. 96.698

Crude material, not distillable nn 1.5503.

: Yield based on epichlorohydrin charged. b Crude product crystallized and was recrystallized from hexane.

This thermal decomposition, if desired, may be used as an efiicient and prabably the most economical method of preparing allyl thiolcarbanrates, which are products of established utility. (See, for example, British patent 808,- 753.)

(II) Illustrative procedures Method A To a well-stirred mixture of 38.0 g. (0.5 mol) of carbon disulfide and 46.3 g. (0.5 mol) of epichlorohydrin in an ice-salt bath is added 36.5 g. (0.5 mol) of anhydrous diethylamine during 1-2 hours at 0 to -5. The mixture is stirred an additional 30 minutes, then let warm slowly to (III) Herbicidal use Pre-emergent herbicidal activity was evaluated by means of the following procedure; I

A solution was prepared by dissolving 290 mg. of the compound to be tested in 200 ml. of acetone. Disposable paper half-flats were prepared and seeded, then sprayed with the acetone solution at therate. of 20 pounds of active chemical per acre of sprayed area. One fiat, which had been seeded with alfalfa, brome, flax, oats, radishes and sugar beets was held at F. day temperature; another seeded with corn, coxcomb, cotton, crabgrass, millet and soybeans was held at F. T wenty-one days after room temperature. At this point the reaction mixture is 75 seeding and treatment the flats were examined and plant emergence and eifects on growth were rated according to the schedule set forth below.

particularly in corrosion-inhibiting formulations, alone or in combination with nitrogen bases of the polyamine type, and as fungicides. The compounds derived from the higher Type of a tion; Degree molecular Weight secondary amines in general exhibit C= h1 rosis (bleaching) 0=n effe t, 5 microbiological activity without substantial effect on N=necrosis l=slight effect. P ant lif G=growth inhibition 2=moderate effect. What I Claim d is: F=formative effect (abnormal 1. The method of combating weeds which comprises form of growth) 3= vere effect, applying to the locus of the weed seeds a herbicidally K=n n-em r n e 4=maximum effect 10 effective amount of a compound represented by the (all plants died). structural formula K i 3 Following are tabulated the results of tests according to the above procedures on a representative group of thiolcarbamates. l 5

PRE-EMERGENT HERBICIDAL ACTIVITY Compound II N-CSOHgCI-l 0H2 Crab- Cox- So Rad- Sugar R R grass comb Brome Millet bean Cotton Alfalfa Oats Corn Flax i511, beet Ethyl Ethyl G1 G1 F1 0 K3 F1 0 G1 0 G1 0 0 0 0 Isopropyl lsopropyl F1 0 G1 K4 G2 G1 0 0 G3 0 0 0 0 Propyl Propyl G3 G3 F2 .1 F3 G1 K4 F3 G1 G1 0 K4 0 0 G3 G1 Hexyl. Hexyl 0 0 0 0 0 O 0 0 0 0 0 0 Butyl 1. Ethyl G2 G2 G1 F2 0 K4 F2 0 0 F1 K4 0 0 0 G1 Iso r0 1 do G1 P W 0 0 K4 0 F1 0 F1 G2 0 0 0 0 Cyelohexyl Isopropyl G1 D0 Ethyl G1 Isobutyl Isobutyl K3 Isopentyl Isopentyl .1 0 0 Allyl- Allyl G1 G3 Cyclohexyl Methyl Isopropyl Isopropyl 0 0 Pro yl .1 Pro yl G3 p p F2 G1 Ethyl Isopropyl 0 0 Butyl Ethyl G3 Cyclohexyl .do v K3 G3 G2 G3 Isobutyl Isobutyl K3 G1 G1 G3 Butyl Butyl K2 K3 K2 G2 G3 G2 G1 K3 G2 G2 G1 F1 G3 0 G2 G2 G2 G1 K4 c1 0 01 G2 0 0 0 G2 '154 "6 "6 Ga er "6 "i1 "6 "G2 K2 G1 G1 G1 0 0 0 o 0 G2 The tabulated data indicate clearly the pronounced selectivity of the pro-emergent herbicidal action of the compositions. Also demonstrated in the data is an absence of activity toward the test species when the N-substituents contain a total of twelve carbon atoms. Although lacking in the desired type of herbicidal activity, the higher N,N- dialkyl-thiolcarbamates are useful for other purposes,

in which R and R represent hydrocarbon substituents having from one to six carbon atoms and containing a total of less than ten carbon atoms.

2. The method of combating weeds which comprises applying to the locus of the weed seeds a herbicidally effective amount of 2-chl0ro-3-me1'capt0propyl N,N-di- 75 propylthiolcarbamate.

3. The method of combezing weeds whiizh co nprises I FOREIGN8PATENTS pfopylthiolcalbamatfi- JAMES O. THOMAS, JR., Primary Examiner References Cited 5 U5, CL X R UNITED STATES PATENTS 252-388, 390; 260-327, 455; 424 275, 286

3,318,676 5/1967 Harman et a1. 71100 @1 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 2 561 949 Dated Februarv 9. 1971 Inventor(s) William Carter Doyle, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Table I, under B.P. or M.P. line 9 "140 44/0.3. 0 .45 mm" should read -l40 55/0.3 0.45 rum-- to be correct. Under the heading Pre-Emergent Herbicial Activity, Cyclohexyl Isopropyl, cotton, "K2, G2", should read -0--to be correct.

Under the heading Pre-Emergent Herbicial Activity, Isobutyl, Isobutyl, Alfalfa, "K4",should read -Gl to be correct.

Under the heading Pre-Emergent Herbicial Activit Isobutyl, Isobutyl, Oats "0" should read K4- to be correct. Column 6, line 72, the word, "weeds" should read, -unwanted grassesto be correct. Column 6, line 73, the word, "weeds" should read ---grass to be correct. Column 7, line 1, the word, "weeds" should read -unwanted grassesto be correct. Column 7 line 2, the word, "weed", should read -grassto be correct.

Signed and sealed this 9th day of November 1971.

(SEAL) Attest:

EDIIARD M.FLE'ICHER,JR. ROBERT GOTTSCHALK Atteating Officer Acting Commissioner of Pat 

